1. Field of the Invention
The present invention relates to woven diaphragms and, more especially, to woven diaphragms that are particularly well adapted for the electrolysis of hydrochloric acid.
2. Description of the Prior Art
Electrolysis of hydrochloric acid is a well-known process (cf., for example, Proceedings of the Electrochemical Society, Vol. 84, 11 (1984), pages 259 et seq.), particularly for producing gaseous chlorine. Plants exist in the majority of industrial nations as means for making valuable use of hydrochloric acid generated by absorption of gaseous hydrogen chloride with water, the gaseous hydrogen chloride being an unavoidable by-product of many organic and inorganic chemical syntheses.
In this process, the electrolysis cells consist of an assembly of the filter-press type; the anode and cathode compartments are separated by a diaphragm, made of polyvinyl chloride in most cases, to avoid mixing of the chlorine and hydrogen produced.
While, in general, the electrolyzer operates satisfactorily, operation of the cell must nevertheless frequently be ceased as a result of the excessive flow of the gases from one compartment into the other, leading to the formation of an explosive mixture of chlorine and hydrogen.
As is apparent from U.S. Pat. No. 3,855,104, the weak point of these electrolyzers is the diaphragm, which is a cloth made of polyvinyl chloride. While these materials are considered to be the most suitable for this purpose, they present many disadvantages in use, among which there may be mentioned:
(i) their embrittlement by chlorination within the electrolysis cell;
(ii) their pronounced tendency to tear and become perforated, particularly along the horizontal folds which are formed when the electrolyzer is in operation; and
(iii) their lack of mechanical strength.
These disadvantages result in premature wear of the diaphragms, which are then incapable of fulfilling their separating function. Not only can the purity of the gases produced no longer be ensured, but mixing thereof can reach a limit which is unacceptable for safety reasons. Furthermore, the flow of chlorine into the cathode compartment leads to an increase in the energy consumption.